Process for dewaxing oils



Patented Apr. 6, 1954 PROCESS FOR DEWAXIN G OILS Harold C. Myers, Woodbury, N. J., assignor to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application February 7, 1952, Serial No. 270,510

Claims. (Cl. 196-48) This invention relates to the separation of wax from wax-oil mixtures, and is more particularly concerned with a process for dewaxing waxcontaining hydrocarbon fractions. More specifically, the present invention provides an improved solvent dewaxing process.

As is well known to those familiar with the art, at dewaxing temperatures, wax-containing hydrocarbon fractions will contain particles of solid wax. Accordingly, several processes have been proposed for effecting the removal of the solid wax particles from the hydrocarbon fractions containing them. In the processes known to the art as dewaxing, recourse is had to filtration and centrifugation to effect the removal.

The dewaxing processes of the prior art may be classified into three main classes which, for convenience, may be enumerated as follows:

1. Filter press dewaxing of low-viscosity waxcontaining oils with or without dilution with a suitable diluent or solvent.

2. Centrifuge dewaxing of high-viscosity waxcontaining oils diluted with a suitable diluent or solvent.

3. Solvent dewaxing of lowor high-viscosity wax-containing oils:

A. Employing filtration for separating Wax and.

oil;

B. Employing centrifugation for separating Wax and oil.

Filter press dewaxing of low-viscosity wax-containing oils comprises chilling a wax-containing hydrocarbon fraction having a S. U. V. of about '7580 seconds at 100 F., to a temperature slightly below that at which the dewaxed hydrocarbon fraction should flow and, thereafter, subjecting the thus chilled hydrocarbon fraction to a filter pressing operation to separate, from the hydrocarbon fraotion, the wax which has precipitated during the chilling operation. Filter press dewaxing is frequently employed in conjunction with naphtha as a diluent for the stock to be dewaxed, especially when high wax-content stocks are being processed or when low oil-content waxes are desired. However, filter press dewaxing is not applicable to the treatment of heavy oils. This is due to the difficulty of filtering oil through the cake formed by the fine crystals of ceresin waxes present in these heavy oils.

Centrifuge dewaxing comprises passing continuously a chilled solution of residual oil in naphtha through a centrifuge revolving at about 17,000 R. P. M., separating the oil and wax streams, and, subsequently, removing the solvent naphtha therefrom. Centrifuge dewaxing is generally applicable to the treatment of residual oils. This is due to the large crystal structure and the resulting poor flow characteristics of the parafiin waxes present in low-viscosity oils. However, with suitable modifications, centrifuge dewaxing can be applied to the processing of distillate oils. Moreover, centrifuge dewaxing has the disadvantage of producing high oil-content waxes and oils which, on standing, sometimes develop wax clouds due to inefiectual dewaxing of the wax-containing residual oil.

The availability of new solvents having given desired characteristics at moderate cost had led to the development of numerous types of solvent dewaxing processes. In general, in these processes, the wax-containing oil is mixed with prescribed amounts of a solvent or diluent and the mixture is chilled to a predetermined temperature. The chilled mixture is then subjected either to a filtering operation or to a centrifuging operation to separate from the oil the wax which has precipitated during the chilling operation. Finally, the solvent is stripped from the wax and from the dewaxed oil.

The benzol-ketone dewaxing process is typical of the solvent dewaxing processes, and probably, is the most extensively used in the petroleum industry for dewaxing both lowand highwiscosity Wax-containing oils and for deoiling the waxes thus obtained in rerun processing. In this process, waxy oil or oily wax admixed with a solvent containing about 40 per cent methylethyl ketone, 52 per cent benzol, and 8 per cent toluol, in a proportion of about 1:3, is chilled to the dewaxing or deoiling temperature by exchange with outgoing products and by refrigeration. Oily and waxy materials are separated by employing a rotary drum-type filter and each is subsequently stripped free of solvent. Dewaxing operationsare carried out at temperatures of about minus 30 F. to about plus 20 F., while wax deoiiing operations are performed at temperatures as high as F. Generally, dewaxing temperatures are about 20 F. lower than the pour point of the finished oil.

Another Widely used solvent dewaxing process is the propane dewaxing process. Propane dewaxing differs from other solvent dewaxing processes in that a liquefied hydrocarbon is utilized in pressure equipment. Chilling to temperatures about 30-40 F. lower than the pour point of the finished oil is effected by self-evaporation of the propane combined, when desirable, with extraneous refrigeration. Filtration is performed with rotary or leaf-type pressure filters. The proportions of solvent to oil are similar to those employed in the benzcl-ketone process and the dewaxing or deoiling temperatures vary from about minus 40 F. to about plus 100 F.

Other solvent dewaxing methods such as the Separator-Nobel and Bari-Sol dewaxing processes, utilize centrifuges for separating oil and Wax from solvent-dilu ed wax-containing oils. The former process employs trichloroethylene as the solvent While the latter utilizes a mixture of benzene with ethylene dichloride as the solvent. In general, the dewaxing or deoiling temperatures are about 20 F. lower than the desired pour point of the dewaxed oil. Solvent-to-oil ratios may be as high as 8:1.

More recently, new processes for dewaxing wax-containing mineral oils have been proposed. In general, in these processes waxy oil is emulsified in various aqueous and/or non-aqueous media, the emulsion is then chilled, and, subsequently, oil is leached from the emulsion.

It is well known that there are numerous disadvantages associated with current methods of removing wax from mineral oils. These disadvantages may be classified into two main groups, i. e., those of an operating nature and those of an economic nature. Accordingly, any process which substantially eliminates the inherent technological difficulties and minimizes the operating costs of the processes of the prior art is manifestly highly desirable.

In copending application for patent, Serial No. 119,502, filed by Myers, Pukkila and Barnes, on October 4, 1949, it was found that the afiinity between the wax and the oil could be materially reduced through the conjoint use of specified surface active agents and of non-freezing aqueous solutions, thereby increasing appreciably the pressed oil rates and diminishin the oil-contents of wax cakes. In this copending application for patent, there is claimed a wax filter pressing process which comprises adding specified amounts of an aqueous solution which is capable of remaining in substantially the liquid state at the pressing temperature, to a wax-oil mixture; treating the resulting mixture in the presence of specified amounts of specified surface active agents, to produce a dispersion of the aqueous solution in th wax-oil mixture; cooling the dispersion to the pressing temperature; and subjecting the dispersion to a wax filter pressing operation.

It has now been discovered that, in the filtration operation of solvent dewaxing processes, satisfactory rates of filtration and reduction of the oil-content of the wax are obtained without the use of anti-freezing agents, i. e., the aqueous phase may be partially or totally frozen during the filtering step.

Therefore, it is a broad object of the present invention to provide a process for separating oil from wax-oil mixtures. Another object is to provide an improved solvent dewaxing process. A more specific object is to improve the filtering operations of solvent dewaxing processes. An important object is to reduce the oil-content of wax obtained from the filtering operations of solvent dewaxing processes. A very important object is to increase the filtered oil rates in the filter operations of solvent dewaxing processes. Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description.

In accordance with the process contemplated herein, it is believed that the afiinity between the wax and the oil-solvent mixture is materially reduced through the partial wetting of the wax crystal surfaces by water. For the primary purpose of providing a more complete understanding of thescope of the present invention, but without any intent of limiting the same, the mechanism whereby wax crystal surfaces are wetted by water, in the presence of oil-solvent mixtures, stripped to its essentials, may be postulated to be as follows: In general, a surface active agent is considered to be a compound, usually an organic compound, one extremity of a molecule of which is polar in nature, in this .instance hydrophilic or oil-repellent, while the other is non-polar in nature, in the present case, hydrophobic or oil-avid. Since wax is essentially oily in character, it follows that, with respect to the non-polar end of a molecule of a surface active agent, there will be competition between wax and an oil-solvent mixture. Conceivably, a surface active agent can be chosen or prepared, a molecule of which possesses a nonpolar end which is more avid for Wax than for oil-solvent mixture. Therefore, in a system consisting of a wax phase dispersed in an oilsolvent phase, the molecules of such a surface active agent will adsorb at the wax-oil-solvent mixture interfaces. This, in effect, means that the wax surfaces are coated, at least in part, with a water-avid or oil-repellent film. Hence, when water is added to the system as a third phase, Water becomes attached to the wax surfaces. The resulting system then will consist of wax particles at least partially covered with water dispersed in a continuous oil-solvent phase. Hence, whereas in a system consisting of a wax phase dispersed in an oil-solvent phase, the latter phase completely envelops and wets the entire surface of each wax particle, in the system modified through the conjoint addition thereto of water and of a surface activ agent, since at least portions of the wax surfaces are covered with water, the oil-solvent phase cannot and will not envelop and wet the entire surface of each wax particle. It follows that the afilnity between the wax and oil-solvent is materially reduced.

In filtering operations, the dewaxed oil-solvent mixture is caused to move through the interstices of the wax cake, by an imposed difference in pressure. Since the interstices are in effect long, winding, capillary channels, considerable resist ance to flow is encountered by the dewaxed oilsolvent. It follows that, other variables remain ing constant, the rate of flow of the dewaxed oilsolvent varies inversely as the viscosity of the dewaxed oil-solvent and varies directly as the slip coefiicient between dewaxed oil-solvent and wax. As set forth hereinbefore, in the filtering operations of the solvent dewaxing processes of the prior art, the dewaxed oil-solvent is directly in contact With the solid wax and the great aflinity of oil-solvent for wax results in zero slip at the interfaces therebetween. In accordance with the present invention, the dewaxed oil-solvent will be in contact with water and since a large amount of slip is known to take place at oil-water interfaces, a reduction in resistance to flow inevitably follows. The obvious result is that the passage of oil-solvent through a wax cake, other variables remaining constant, is greatly facilitated and that the oil-content of the wax cake is greatly reduced.

Accordingly, and broadly stated, the present invention provides an improved solvent dewaxing process, which comprises adding specified amounts of water to a wax-containing oil-solvent mixture, treating the mixture thus obtained in the presence of specified surface active agents in amounts to disperse the aqueous solution in the oil-solvent mixture. chilling the mixture to dewaxing temperature, and subjecting the chilled mixture to a filtering operation.

In general, any wax-containing oil or any oilcontaining wax is amenable to the process of the present invention. The wax-containing oil ordinarily is a petroleum stock, although other Waxbearing oils, such as brown coal tar oils, shale oils, and synthetically produced oils, any of which may have been previously subjecting to a deasphalting treatment or other treatment for the purpose of improving their physical and/or their chemical nature may be mentioned by Way of non-limiting examples of materials suitable as charge stocks for the process contemplated herein. There appears to be nothing critical in the amount of wax present in the wax-containing oils to be treated. Thus, the wax-content of the charge stocks may vary between about 0.1 per cent and about 99.9 per cent by weight. On the other hand, the amount of wax present in either of the mixtures is largely determinative of the fluidity of the charge to the process.

Accordingly, in practicing the invention and as is well known in solvent dewaxing operations, the fluidity of the charge to the process is increased by the addition of an oil-miscible solvent which will lower the viscosity of the oil. The solvents which may be used herein are those well known in the prior art. A suitable solvent, in general, should possess the following properties. It should :be substantially completely miscible with .the stock to be treated, it should be substantially insoluble in and immiscible with water, it should possess, preferably, a low viscosity coefiicient, it should not manifest any substantial tendency to em-ulsify under the conditions of the process, it should be a poor solvent for solid wax at the dewaxing temperature, it must not disturb the adsorption of the molecules of the surface active agent at the solid wax surfaces, it must not affect, to any appreciable extent, the tendency of the surface active agent to adsorb at the solid wax surfaces, and, finally, it should not displace water from the waterwetted wax surfaces. Propane, methyl-ethyl ketone, trichloroethylene, ethylene dichloride, and mixtures, such as methylethyl ketone-benzene mixtures, ethyl carbonate-propane mixtures, and ethylene dichloride-benzene mixtures may be mentioned by way of non-limiting examples of solvents suitable for the purposes of the present invention.

There appears to be nothing critical in the amounts of solvent used. Accordingly, the amounts of diluent used may vary between wide limits. Ordinarily, amounts to produce between about a 0.1 1 and about 20 1, preferably, between about 2 1 and 4 z 1 (volume of solvent to volume of charge stock), dilution are employed. In practice, the solvent is added usually prior to or during the chilling step.

Generally speaking, the surface active agents utilizable herein are those which are known as such in the art. As stated hereinbefore, the surface active agents are characterized :by molecules having a hydrophobic group (the non-polar group) and a hydrophilic group (the polar group). The surface activity of the molecule in an aqueous-non aqueous system, such as exists in the process of the present invention, is due to the adsorption of the molecule at an interface. In general, it may be stated that the preferred surface active agents applicable herein are those in which the hydrophobic portion of the molecule is hydrocarbon-like in nature and the hydrophilic portion is a radical selected from the group consisting of -OH, SOaI-I, COOH, CO, NI-Iz, NOz, N.N-, N N.N, CSNH, CONHX, COO, PO4, POaHz, POaH, COC, 'SO4M and SOsM, wherein M is the hydrogen equivalent of a metal. These criteria, therefore, aiford the basis for a classification of the various types of surface active agents suitable for the purposes contemplated herein. For ponvenience, the types may be tabulated as folows:

TABLE I Types of surface active agents TYPE A Group Name Formula of an Example Fatty acid salt Dm eltal salt of a sulfated fatty ac Glyceryl ester of a fatty acid. Metal sulionate of a fatty acid ester. Metal dsulfonate of a fatty acid am e. Fatty acid amide ethyl dialkyl amine.

RC O ONa RCnHal- (SO4Na)COONa RCOOCHzCHOHCHzOH ROOOOHzOHzSOsNai.

Quaternary ammonium halide.

Type

Natural substances .l

'Wherein R, R, R and R' are alkyl or alkenyl radicals, X is a halogen, and n is a whole number.

A number of surface active agents representa- Efiective surface active agents Chemical Name or Formula Trade Name 2. CHaCH(GH|) Nekal A.

O S O :Na

Nekal B.

O S O :No

CuHrssOiNa C17H34SO4N3 Sodium wax phenol sulfonate. Sorbitan monstearate CuHnC aHz( O H)S OaNa. CoHnCnHa(OH)SO:NB (C isHaflsC 11H( 0 H) S OzNa- Tergitol 4. Tergitol 7.

Span 60.

Sorbitan is derived from the dehydration of sorbitol to cause ring closure, through an ether linkage, to produce a six-member or a five-member ring.

The surface active agents enumerated in Table II are illustrative of specific surface active agents operable in the process of the present invention. Wax aromatic sulfonates or wax oxyaromatic sulfonates and alkali metal salts of sulfated fatty acids are typical of two of the preferred classes of surface active agents to be used herein and in order to furnish the criteria to be applied in the selection of a surface active agent which will give optimum results with a given charge stock, further discussion of surface active agents utilizable herein will be had in conjunction with alkali metal salts of wax-aromatic sulfonic acids.

Materials known as wax-phenol sodium sulfonate, for example, may be prepared, as is well known in the art, in accordance with the following procedure (U. S. Patent to Reiif et al., No. 2,252,666) A paraffin wax melting at about 120 F. and predominantly comprised of compounds having at least 20 carbon atoms per molecule is chlorinated by heating to about 200 F. and bubbling chlorine therethrough until the chlorwax obtained contains from about 10 per cent to about 21.-per cent by weight of chlorine. The chlorwax is then condensed with phenol, at a temperature of about 350 F. and in the presence of about 4 per cent to about 10 per cent by weight of an aluminum chloride Friedel-Crafts catalyst, to produce wax-substituted phenol. This product is treated with chlorosulfonic acid in amounts, on a weight basis, of about -175 per cent of theoretical, in a conventional sulfonation operation, at a temperature of about -4200 F. and the product thus obtained is neutralized with sodium hydroxide in amounts, on a weight basis, of about 120-150 per cent of theoretical, at a temperature of about F.

In general, the structure of materials known as wax phenol metal sulfonates is visualized to be as follows:

wherein R may be wax or other hydrocarbon radical of comparable chain length, M is the hydrogen equivalent of a metal, and n is 1 to 3. The wax groups may be derived from a fraction of a viscous mineral oil ranging in molecular weight from that of a light wax distillate to a heavy residuum. The primary factor to be considered in determining the value of 11. is the resulting solubility of the compound in water.

Materials known as wax phenol (1-14) sodium sulfonate are a good example of a surface active agent useful in the process of the present invention. With respect to the connotation (1-140, the first number indicates the theoretical degree of alkylation, i. e., the atomic proportions of chlorine in the chlorwax which is reacted with one mole of the hydroxy-aromatic compound, and the second number indicates the weight per cent of chlorine in the chlorwax. The wax phenol (1-14) sodium sulfonate actually is a mixture of the mono-wax phenol sulfonate, the diwax phenol sulfonate, and of some poly-wax phenol sulfonates.

The test for determining whether a surface active agent will be operable or not in the process of the present invention is the bubble machine test [see Engineering and Mining Journal, 137, 291 (1936)] equipped with a cold stage. In this test, a piece of wax of the type to be removed and having at least one relatively flat surface is immersed in the oil-solvent mixture to be dewaxed containing 0.1 per cent by weight of the surface active agent to be tested. A droplet of water containing 0.1 per cent by weight of the surface active agent to be tested is placed in a bubble holder and the droplet is then permitted to come into contact with the wax surface. If a finite three-phase (from wax through oilsolvent to water) contact angle can be measured, the surface active agent being tested will be operable in the process of the present invention. The larger the three-phase contact angle, the more effectual the surface active agent will be in the process. Therefore, if the water spreads over the entire fiat wax surface (contact ang1e=180), the surface active agent being tested will be very effectual. Accordingly, the surface active agents operable herein can be defined as those which produce a finite threephase contact angle in the bubble machine test.

Using the bubble machine test, a number of surface active agents were tested with the following results:

TABLE III Three-Phase Contact Angle Surface Active Agent M Paraffin 1cm? crystalline Wax Wax Degrees Degrees Sodium Wax Phenol Sulfonate (1-14) 17 17 Tergitol 7. 22 10 Tergitol 4 22 10 Span 60 50 50 Nekal A. 43 1 N ekal B l 47 10 CnHzNaHflOH) SOsNa 36 10 CvH1nCsHa(OH)SOaNa 24 10 (CisHs7)sCtH(OH)SO3Na 24 10 0 (C1sH:7)2P 60 10 0 [CH:(|3H( CH2)4]2P\ 30 10 CaHs OH The amounts of surface active agent to be used may vary between wide limits. Excessive amounts are to be avoided since, as might be expected, it has been found that they efiect emulsification 0f the oil-solvent mixture in the aqueous phase. On the other hand, the use of insufiicient amounts will result in indifferent results. In general, the amounts of surface active agent to be used depend upon the amount of wax present in the stock undergoing treatment. Obviously, the optimum amounts to be utilized in any given instance can be readily determined by those skilled in the art by a few preliminary tests. In practicing the invention, it has been found that amounts varying between about 0.1 per cent and about 5 per cent, preferably, between about 0.25 per cent and about 2.5 per cent, based on the weight of the wax-containing oil or oil-containing wax in the charge will produce satisfactory results.

The surface active agent is ordinarily added to the charge as a solution in water. In conformance with the mechanism of operation postulated hereinbefore, the water is an essential factor in the successful operation of the process of the present invention. The wax surfaces will be at least partially covered, ultimately, with Water or aqueous phase. The amounts to be used depend, of course. upon the amount of wax present in the stock undergoing treatment. Obviously, the optimum amounts to be utilized in any given instance can be readily determined by those skilled in the art by a few preliminary tests. In practice, it has been found that amounts varying between about 2.5 per cent and about 100 per cent, preferably, between about 5 per cent and about 25 per cent, based on the weight of the wax-containing oil-solvent mixture in the charge will produce satisfactory results.

Agitation is necessary to effect dispersion of the aqueous phase in the wax-bearing oil-solvent mixture and to ensure collision between the dispersed aqueous phase and wax particles during and after chilling. In order to facilitate the dispersion of the aqueous phase in the wax-oilsolvent mixture and to ensure that the wax-oilsolvent mixture constitutes a homogeneous liquid phase at the beginning of the treatment, it is Ordinarily preferred to heat the mixture to tem- -10 peratures varying between about 100 F. and about 200 F. during the dispersion operation. The temperature to be utilized to produce optimum results will depend upon the nature of the stock undergoing treatment.

The filtering temperatures applicable in the process are those of the prior art, i. e., between about 30 F. and about 20 F. It must b recognized, of course, that the filtering temperature applicable in any particular instance will depend upon the nature of the system, i. e., the surface active agent utilized, the type of dewaxing solvent, etc.

The rate at which the temperature of th mixture is lowered to dewaxing or filtering temperature (the chilling rate) is not a critical factor, although, as it will be appreciated by those skilled in the art, an important factor. The chilling rate, as is well known, is largely determinative of the size of the wax crystals that precipitate out during the chilling operation. For general purposes it has been found that an average chilling rate of about 100 F. per hour to about 800 F. per hour is conducive to optimum results.

Although the foregoing discussion has indicated a preferred sequence of the addition of the various components to the system and of the manipulations involved in the process, it must be clearly understood that departures from them may be made. For example, the wax-oil mixture and the oil solvent may be separately chilled and then mixed at any temperature down to the de waxing or pressing temperature.

The following examples are for the purpose of illustrating modes of carrying out the process of the present invention and to point out the ad vantages thereof, it being understood that the invention is not to be considered as being limited to the specific stocks, surface active agents, and solvents or to the manipulations, apparatuses, and conditions set forth therein. As it will be apparent to those skilled in the art, a wide variety of stocks, surface active agents, and solvents and a diversity of apparatuses, manipulations and conditions, as described hereinbefore, may be employed to carry out the filtering operation.

Example l.--C'orwent onal filtering of crystalline wax One volume of a furfural-refined, waxy distillate having a Saybolt Universal viscosity of 42.5 seconds at a temperature of 210 F. was mixed with 2 volumes of a solvent composed of 50% benzol, 40% methyl-ethyl ketone and 10% toluene. The resulting mixture was chilled to 0 F. and filtered on a 5-inch, brine-jacketed metal funnel containing No. 2 grade filter paper. A filtration curve (time versus volume of filtrate) was determined at a vacuum equivalent to 12.5 inches of mercury. From this curve, the filter rate was calculated as 5.06 gallons'of dewaxed oil per square foot per hour. The wax cake contained 68% by weight of oil and the dewaxed oil had a pour point of 20 F.

Example 2.-E17ect of water The run described in Example 1 was repeated but with the addition to the mixture of 0.0516 volume of water. The flow of filtrate through the wax cake stopped after the filtration was only complete.

Example 3.E1fect of surface active agent The run described in Example 1 was repeated but with the addition to the mixture of 0.5% by weight based on the oil of wax-phenol (1-14 11 sodium sulfonate derived from distillate stock wax. A filter rate of 2.46 gallons of dewaxed oil per square foot per hour was obtained.

Example 4.E,fiect of water and surface active agent The run described in Example 1 was repeated but w th the addition to the mixture of 0.0525 volume of water and. of 0.5% by weight based on the oil of wax-phenol (1- 4) sodium sulfonate derived from distillate stock wax. A filter rate of 28.5 gallons of dewaxed oil per square foot per hour was obtained. The wax cake contained 29.4% by weight of oil and the dewaxed oil had a pour point of 15 F.

Example 5.-Efiect of non-freezing aqueous solution and surface active agent The run described in Example 1 was repeated but with the addition to the mixture of 0.06 volume of a 60% water-49% ethylene glycol (antifreezing agent) solution and of 0.6% by weight based on the oil of wax-phenol (1-14) sodium sulfonate derived from distillate stock wax. A filter rate of 28.5 gallons of dewaxed oil per square foot per hour was obtained. The wax cake contained 33.3% by weight of oil and the dewaxed oil had a pour point of 20 F.

It will be noted that the addition of water alone interferes with the filtration operation seriously. The addition of a surface active agent, in the absence of water, reduces the filter rate materially. The conjoint use of Water and of a surface active agent, however, produces almost a six-fold increase in the filter rate, a 56 per cent reduction in the oil-content of the wax cake, and an appreciable decrease in the pour point. On the other hand, the conjoint use of a non-freezing aqueous solution and of a surface active agent although producing almost a six-fold increase in the filter rate, effects only a 36 per cent reduction in the oil-content of the wax cake and no decrease in the pour point of the oil.

Example 6.-Conventicmal filtering of microcr'ystalline war The run set forth in Example 1 was repeated but in this case, the charge consisted of the solvent and a propane-deasphalted, furfural-refined waxy residual oil having a Saybolt Universal viscosity of 128.6 seconds at a temperature of 210 F. in a solvent to oil ratio of 4.2:1. A filter rate of 3.34 gallons of dewaxed oil per square foot per hour was obtained. The petrolatum contained 27.3% by weight of oil and. the dewaxed oil had a pour point of 20 F.

Example 7.-E17ect of water and surface active agent The run described in Example 5 was repeated but with the addition to the mixture of 0.06 volume of water and of 0.66% by weight based on the oil of wax-phenol (1-14) sodium sulfonate. A filter rate of 8.64 gallons of dewaxed oil per square foot per hour was obtained. The petrolatum contained 20.1% by weight of oil and the dewaxed oil had a pour point of 20 F.

Example 8.-E1'fect of non-freezing aqueous solution and surface active agent The run described in Example 5 was repeated but with the addition to the mixture of 0.6 volume of a 60% water-40% ethylene glycol (antifreezing agent) solution and of 0.8% by weight based on the oil of wax-phenol (1-14) sodium sulfonate. A filter rate of 7.08 gallons of dewaxed oil per square foot per hour was obtained. Thepetrolatum contained 23.1% by weightof 'oil and the dewaxed oil had a pour point of 20 F.

It will be noted that the conjoint use of water and of a surface active agent produces more than a two and a half fold increase in the filter rate and a 26 per cent reduction in the oil-content of the petrolatum. On the other hand, the conjoint use of a non-freezing aqueous solution and of a surface active agent produces a two-fold increase in the filter rate and a 15 per cent reduction in the oil-content of the petrolatum.

The following examples illustrate the utilization, in the process of the present invention, of surface active agents other than wax-phenol (1-14) sodium sulfonate derived from distillate stock wax. In each example, the run described in Example 1 was repeated but with the addition to the mixture of 0.06 volume of water and of 0.6 per cent by weight based on the oil of a surface active agent. For convenience, the pertinent data of the runs of Examples 9, 10, 11 and 12 are set forth in the following table:

suli onate sulionate Filter Rate, gals. per sq. ft.

per hour 6.5 7.2 16.8 10.6 Dewaxed Oil, Pour Point,

O F 15 20 15 20 Wax Cake, Oil-Content,

percent wt 59. 5 55. 7 36. 8 44. 4

In view of the foregomg, 1t W111 be appreciated by those skilled in the art that surface active agents operable in the process contemplated herein may be present in or may be introduced into the system through the wax-oil mixture or through the solvent. These contingencies can be readily established through a bubble machine test carried out in the absence of an added surface active agent. AccordinglyJt must be clearly understood that when in the specification and in the claims hereof, the presence of a surface active agent is referred to, either the introduction of a surface active agent into the system through these contingencies or the actual addition of a surface active agent to the system, or both, is intended.

It will be apparent that the present invention provides an improved solvent dewaxing process. It will be appreciated by those skilled in the art that the present invention may be embodied in other specific forms Without departing from the spirit or essential attributes thereof. Accordingly, it must be clearly understood that the present embodiments be considered in all respects illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

What is claimed is:

1. An improved solvent dewaxing process which of a surface active agent that produces a finite three-phase contact angle in the bubble machine test, in amounts of at-leastjabout 0.1 per cent, based on the weight of the wax-oil mixture, but less than the amount necessary to promote formation of a wax-oil-solvent mixture-in-water emulsion in which the water is the continuous phase, to produce a dispersionin which the water is the dispersed phase and the wax-oil-solvent mixture is the continuous phase; cooling said dispersion to the filtering temperature to precipitate wax and to freeze at least partially said water; continuing said treating to associate said wax with said dispersed phase, thereby producing a dispersed waxat least partially frozen water phase; and subjecting said dispersion to a filtering operation. f

2. An improved solvent dewaxing process which comprises adding water to; a solvent-wax-oil mixture, in an amount varying between about Per cent and about 25 percent, based on the weight of the wax-oil mixture, to produce a watersolvent-wax-oil mixture; agitating said water-solvent-wax-oil mixture in the presence of an alkali metal salt of a -wax-substituted aryl sulfonate that produces a finite three-phase contact angle in the bubble machine test in amounts varying between about 0.25 per cent and about 2.5 per cent based on the weight of the wax-oil mixture, to produce a dispersion in which the water is the dispersed phase and the solvent-waxoil mixture is the continuous-phase; cooling said dispersion to the filtering temperature to precipitate wax and to freeze at'least partially said water; continuing said agitating to associate said wax with said dispersed phase, thereby produc-' ing a dispersed waxat least partially frozen water phase; and subjecting said dispersion to a filtering operation. I,

3. An improved solvent dewaxing process which comprises adding water to a wax-oil-solvent mixture, in an amount varying between 5 per cent and about 25 per cent, based on the weight of the wax-oil mixture, to produce a water-waxoil-solvent mixture; agitating said water-waxoil-solvent mixture in the presence of sodium wax-phenol (1-14) sulfonate in amounts varying between about 0.25 per centjand about 2.5 per cent based on the weight of the wax-oil mixture, to produce a dispersion in which the water is the dispersed phase and the wax-'oil-solvent mixture is the continuous phase; cooling said dispersion to the filtering temperature to precipitate wax and to freeze at least partially said water; continuing 14 said agitating to associate said wax with said dispersed phase, thereby producing a dispersed waxat least partially frozen water phase; and subjecting said dispersion to a filtering operation.

4. An improved solvent dewaxing process which comprises adding water to a solvent-wax-oil mixture in an amount varying between about 5 per cent and about 25 per cent, based on the weight of the wax-oil mixture, to produce a watersolvent-wax-oil mixture; agitating said watersolvent-wax-oil mixture in the presence of sodium wax-naphthalene (1-14) sulfonate, in amounts varying between about 0.25 per cent and about 2.5 per cent based on the weight'of the waxoil mixture, to produce a dispersion in which the water is the dispersed phase and the solvent-waxoil mixture is the continuous phase; cooling said dispersion to the filtering temperature to precipitate wax and to freeze at least partially said water; continuing said agitating to associate said wax with said dispersed phase, thereby produc-- ing a dispersed waxat least partially frozen water phase; and subjecting said dispersion to a filtering operation,

5. An improved solvent dewaxing process which comprises adding water to a wax-oil-solvent mixture, in an amount varying between about 5 per cent and about 25 per cent, based on the weight of the wax-oil mixture, to produce a water-wax-oil-solvent mixture; agitating said water-wax-oil-solvent mixture in the presence of sodium wax-phenanthrene (1-14) sulfonate, in amounts varying between about 0.25 per cent and about 2.5 per cent, based on the weight of the wax-oil mixture, to produce a dispersion in which the water is the dispersed phase and-the waxoil-solvent mixture is the continuous phase; coolin said dispersion to the filtering temperature to precipitate wax and to freeze at least partially said water; continuing said agitating to associate said wax with said dispersed phase, thereby producing a dispersed waxat least partially frozen water phase; and subjecting said dispersion to a filtering operation.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,164,013 Jenkins June 27, 1939 2,168,306 Schutte Aug. 1, 1939 2,263,535 Carr et a1. Nov. 18, 1941 2,267,093 Hall et a1 Dec. 23, 1941 

1. AN IMPROVED SOLVENT DEWAXING PROCESS WHICH COMPRISES ADDING WATER TO A WAX-OIL-SOLVENT MIXTURE IN AN AMOUNT VARYING BETWEEN ABOUT 2.5 PER CENT AND ABOUT 100 PER CENT, BASED ON THE WEIGHT OF THE WALL-OIL MIXTURE, TO PRODUCE A WATER - WAX - OIL-SOLVENT MIXTURE; TREATING SAID WATER-WAX-OIL-SOLVENT MIXTURE IN THE PRESENCE OF A SURFACE ACTIVE AGENT THAT PRODUCES A FINITE THREE-PHASE CONTACT ANGLE IN THE BUBBLE MACHINE TEST, IN AMOUNTS OF AT LEAST ABOUT 0.1 PER CENT, BASED ON THE WEIGHR OF THE WAX-OIL-MIXTURE, BUT LESS THAN THE AMOUNT NECESSARY TO PROMOTE FORMATION OF A WAX-OIL-SOLVENT MIXTURE-IN-WATER EMULSION IN WHICH THE WATER IS THE CONTINUOUS PHASE, TO PRODUCE A DISPERSION IN WHICH THE WATER IS THE DISPERSED PHASE AND THE WAX-OIL-SOLVENT MIXTURE IS THE CONTINUOUS PHASE; COOLING SAID DISPERSION TO THE FILTERING TEMPERATURE TO PRECIPITATE WAX AND TO FREEZE AT LEAST PARTIALLY SAID WATER; CONTINUING SAID TREATING TO ASSOCIATE SAID WAX WITH SAID DISPERSED PHASE, THEREBY PRODUCING A DISPERSED WAX- AT LEAST PARTIALLY FROZEN WATER PHASE; AND SUBJECTING SAID DISPERSION TO A FILTERING OPERATION. 